It is so dazzling that there are numerous types of RC lipo battery on the market today. However, the quality of lithium polymer battery is a major worry for aeromodeller, and therefore, we today make popular scientific education about how to evaluate the quality of lithium polymer battery.
Most of current lithium polymer batteries and all the UAV batteries are the battery pack with composition of the connection in series and in parallel, including connection in series presenting as "S" and connection in parallel presenting as "P". For example, 3S battery means 3 chips connected in series, and 6S2P means 12 chips of battery core with 6 chips connected in series and 2 chips connected in parallel.
Why it does need to be connected in series or in parallel?
It is determined by the lithium polymer battery. It is connected in series for increasing voltage, while as connected in parallel for increasing capacity. The C rate of battery will never change with the connection in series or in parallel. The battery with high C rate is used in the low-power equipment, such as remote control and receiving of image transmission, which has no effect on the equipment as long as the voltage does not exceed to damage the equipment.
How to evaluate the quality of single-chip battery core and battery packs?
Performance valuation of single-chip battery core
1.Target rate of C: is the discharge rate can reach the identified rate value of the battery
In accordance with the industry standard, the C rate of a battery is evaluated by discharging with X rate of battery capacity, and the battery discharge is not lower than 3.50V and the discharge curve is smooth around 3.50V. The C rate of the battery is the maximum value of X, which is evaluated by various indicators, including pressure drop, holding capacity of pole piece, temperature, flatulence or not, safety, etc.
2.Target rate of capacity: The capacity can reach the identified capacity value of the battery
In general, high-quality battery core shall be designed with 3%-5% higher than the design capacity, which is used in the high-quality battery chip of China's major plants, with a single capacity around 5200MAH.
There is no standard outlining how long is the cycling life of lithium polymer battery in the current industry, due to the cycling life has a close link with battery production process. Through analyzing the current test data, it indicates that the capacity of the battery is decreased in various degrees by each process of charging and discharging.
Performance valuation of lithium polymer battery packs
High-quality single battery core may not produce a high-quality lithium polymer battery pack, but high-quality polymer battery pack must be composed of high-quality battery cores, which is related to the matching problems. Matching is a very complicated technique with high requirements for the equipment, which requires a battery pack composed of battery cores consistent with all capacity, the C rate and attenuation rate. Life of the battery pack is shortened by a large difference in any one of the three indicators, while as the similar values of the three indicators indicate improved performance of the battery pack to ensure flight safety.
To give an illustration
For example, 30C 3S 5000mAh lipo battery. The battery match with the capacity of three batteries are 5120MAH, 5120MAH and 5320MAH respectively, and all three batteries are charged to 4.20 V. After discharging 5000MAH on the model airplane, the remaining capacity of the three batteries are 120MAH, 120MAH and 320MAH respectively, which causes voltage unbalance in the battery pack by high voltage in the 320MAH battery and low voltage in the other two batteries, as certain relationship between capacity and voltage. In the case of discharging to 5150MAH, two batteries may actually change into reverse charging situation, and it may be wrongly assumed that the battery pack still has power as one battery has voltage, which will definitely affect the life of the battery pack.
This is caused only by the unbalance in the capacity. If there is a large difference in the C rate, it may cause unbalance during the charging process and ultimately affects the battery pack's life, even with the same capacity, which is for the reason that the more discharging rate with a high C rate, and the less power consumption.
Therefore, it is a simple way to evaluate a battery is whether a high-quality lithium polymer battery or not.
Step 1: full of electricity, and make sure every single battery in the same pack with the voltage of 4.20V;
Step 2: install the battery pack on a aircraft and wait for each single battery's voltage around 3.66 V;
Step 3: separate testing the voltage difference on each single battery, and the qualified high-quality battery has the voltage difference in 0.01V.
In addition, single measuring voltage of the high accuracy digital multimeter shall be prevail, and it is better to measure by a digital mutimeter in thousands.